It is known (Bitko, U.S. Pat. No. 3,697,906, issued Oct. 10, 1972) to provide mercury relays and switches employing armatures, in which a metallic enclosure composed of a cap and header welded at their rims form an enclosure and in which the armature is a spiral spring having its center point free to move and its outer perimeter constrained. The inner surface of the enclosure and the armature are mercury wettable. An electrode, mercury wettable at its inner end, extends through one of the cap and header via an insulator into promimity to the center of the armature and is itself magnetic. Application of magnetic force then causes the central free end of the armature to move into contact with the electrode to complete a circuit between the electrode and the enclosure, the insulator being of non-mercury wettable material, preferably glass. Only enough mercury is inserted into the enclosure to form a thin layer of mercury over the mercury wettable surfaces, but not enough to form a pool of mercury.
Use of the specified quantity of mercury renders the switch operable in any orientation and when subjected to high accelerations, since surface tension forces hold the mercury layer in place, and/or cause it to reform if it is broken. Closure of the contacts causes splatter of mercury, but the splattered mercury rejoins the thin layer.
In accordance with the present invention, which relates to a tilt switch, the general concept of employing only enough mercury to form a thin layer in a mercury wettable enclosure is departed from to the extent that an excess of mercury is added, which forms a small pool in the enclosure, in addition to the thin layer, the small pool representing a localized thickening of the mercury layer, the location of which is determined by the force of gravity.
The electrode extends into the pool of mercury when the electrode is vertical, but also when the electrode departs from the vertical within a solid angle determined by the depth of the pool and the length of the electrode and the shape of the enclosure. The present system requires that a circuit be maintained closed over a predetermined and fixed solid angle in the range of 15.degree. - 30.degree. from the vertical, and open otherwise. The use of the invention is to illuminate the LED of a LED timepiece, i.e. a wristwatch, when the latter is held nearly horizontal for observation by a wearer, the LEDs being otherwise unilluminated.
The depth of the mercury pool, when the electrode is vertical, is very precisely established, in accordance with the present invention, and the pool moves precisely according to the angle of a tilt of the electrode, so that it is possible to establish with considerable precision the solid angle over which switch closure occurs and this angle can be as small or as large as desired within wide limits.
The use of mercury contacts provides extremely low and constant contact resistance, and the capability of passing very small currents, of the order of a few microamperes.